Boston bombs: Memorial for slain officer Sean Collier
Thousands of mourners have held a memorial for a university police officer killed during the hunt for the Boston Marathon bombing suspects.
US Vice-President Joe Biden spoke at the service in memory of 26-year-old Sean Collier at the Massachusetts Institute of Technology.
About 4,000 students, staff and police officials from around the country attended the ceremony.
Authorities say Collier was killed by the brothers suspected of the bombing.
Wednesday's service was held as anonymous US officials told the Associated Press that the bombs had been triggered by remote-controlled detonators.
But the devices - which killed three people and injured more than 260 - were not sophisticated and had to be set off within a few blocks of the explosives, said the officials.
Collier had worked for the prestigious university's police department for more than a year and had been involved in campus activities, in addition to his role as an officer.
Queues of mourners stretched for about half a mile (0.8km), an hour before Wednesday's ceremony started.
They made their way through tight security, including metal detectors and bomb-sniffing dogs.
During the ceremony, Collier's brothers thanked police officers and others for their support.
Mr Biden told the family: "My heart goes out to you. I hope you find some solace in this time of extreme grief."
He also said the university's diversity and record of innovation represented a "nightmare" for those who hated and would attack America.
"The only way they can gain ground is to instil fear that causes us to jettison our values, way of life, for us to change," Mr Biden said.
Massachusetts Institute of Technology Police Chief John DiFava remembered how the young officer had once asked to volunteer at a homeless shelter.
"He hoped to 'maybe deal with issues before they became problems'," Chief DiFava said.
Collier was laid to rest in a private funeral on Tuesday.
"He is one of the nicest people that I've ever met," Kelly Daumit, an engineering student who hiked with Collier as part of a university social club, told AP news agency.
"Everything people are saying about him is completely genuine; it's not because of what happened."
Suspects' parents 'interviewed'
Collier was shot dead in his car on 18 April, three days after the bombing.
The shooting led to a huge manhunt that ended in the death of suspect Tamerlan Tsarnaev and the wounding of his younger brother and alleged accomplice, Dzhokhar.
In a court hearing on Monday before a federal magistrate judge at Beth Israel Deaconess Medical Center, Dzhokhar Tsarnaev was charged at his hospital bedside with crimes that could result in the death penalty if convicted.
US officials say the ethnic Chechen brothers planted and detonated two pressure-cooker bombs near the finish line of the Boston Marathon on 15 April. Ten people lost limbs in the bombing.
The area around the marathon finishing line on Boylston Street reopened on Wednesday, nine days after the attacks.
Fresh cement was reportedly still drying on the street as a Starbucks coffee shop reopened for the first time, allowing customers to pick up belongings left behind in the chaos after the bombing.
Many other businesses, banks and restaurants on Boylston Street remain closed.
US investigators are in contact with the bombing suspects' parents in southern Russia, an American embassy official said on Wednesday.
An unnamed official told the AP news agency that US investigators were working with the Russian security services, the FSB.
He would not say how long the Americans planned to stay in Dagestan, a region in the southern area of the country.
The father was quoted as telling the Russian state news agency RIA Novosti that both parents planned to fly to the US on Thursday.